A contour line is a line drawn on a topographic map to indicate ground elevation or depression. A contour interval is the vertical distance or difference in elevation between contour lines. Index contours are bold or thicker lines that appear at every fifth contour line.

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**Example 2**- Draw a profile showing the elevations of the contours.Note: The intervals are increasing, therefore, the contours indicate a hill. The peak is normally considered to be located at half the interval distance.Widely separated contour lines indicate a gentle slope. Contour lines that are very close together indicate a steep slope.The figure above illustrates various topographic features. (b) Notice how a mountain saddle, a ridge, a stream, a steep area, and a flat area are shown with contour lines.The figure above illustrates a depression and its representation using contour lines. Notice the tick marks pointing toward lower elevation.

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Figure One

Figure Two

### SLOPE PERCENT FROM TOPOGRAPHIC MAP

The horizontal distance between points A and B can be measured with a scaled ruler and used to determine the slope percent.slope percent = rise/run × 100Example 4- What is the slope percent in Exercise 2 above?slope percent = rise/run × 100.For this computation, the rise, or vertical ground distance, and run, or horizontal ground distance, are needed.Step 1.Measure the horizontal map distance between points A and B to get the vertical ground distance.The horizontal map distance measures 0.5 inches.Step 2.Use the appropriate conversion factor to convert the horizontal map distance to horizontal ground distance.0.5 in × 24,000 in/in = 12,000 inStep 3.The desired unit is feet. Set up the cancellation table so all units will cancel, except the desired unit, feet.

Step 4.Use the slope percent equation and solve. The run is 1000 feet and the rise in elevation is 120 feet.slope percent = rise/run × 100slope percent = (120ft / 1000ft) × 100 = 12%Slope Worksheet- Use the information from the example above and complete the slope worksheet. Line 1 starts with the contour interval, not the projection point.Slope Worksheet (to be completed)Line | Input | ||

0 | PP | Projection point | ______ |

1 | CON INT | Contour interval, ft | ______ |

2 | SLC | Map Scale | ______ |

3 | CF | Conversion factor, ft/in | ______ |

4 | #INTVLS | # of contour intervals | ______ |

5 | RISE | Rise in elevation, ft | ______ |

6 | MD | Map distance, in (between points) | ______ |

7 | HZGD | Horizontal ground distance, ft | ______ |

Output | |||

SLP% | SLOPE% | ______ |

Slope Worksheet (completed)

Line | Input | ||

0 | PP | Projection point | A-B |

1 | CON INT | Contour interval, ft | 40 |

2 | SLC | Map Scale | 1:24,000 |

3 | CF | Conversion factor, ft/in | 2,000 |

4 | #INTVLS | # of contour intervals | 3 |

5 | RISE | Rise in elevation, ft | 120 |

6 | MD | Map distance, in (between points) | 0.5 |

7 | HZGD | Horizontal ground distance, ft | 1,000 |

Output | |||

SLP% | SLOPE% | 12 |